man/systemd.syntax.xml

   1 <?xml version='1.0'?>
   2 <!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
   3   "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd" [
   4 <!ENTITY % entities SYSTEM "custom-entities.ent" >
   5 %entities;
   6 ]>
   7
   8 <!-- SPDX-License-Identifier: LGPL-2.1+ -->
   9
  10 <refentry id="systemd.syntax">
  11
  12   <refentryinfo>
  13     <title>systemd.syntax</title>
  14     <productname>systemd</productname>
  15   </refentryinfo>
  16
  17   <refmeta>
  18     <refentrytitle>systemd.syntax</refentrytitle>
  19     <manvolnum>7</manvolnum>
  20   </refmeta>
  21
  22   <refnamediv>
  23     <refname>systemd.syntax</refname>
  24     <refpurpose>General syntax of systemd configuration files</refpurpose>
  25   </refnamediv>
  26
  27   <refsect1>
  28     <title>Introduction</title>
  29
  30     <para>This page describes the basic principles of configuration files used by
  31     <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>
  32     and related programs for:
  33     <itemizedlist>
  34       <listitem><para>systemd unit files, see
  35       <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
  36       <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
  37       <citerefentry><refentrytitle>systemd.socket</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
  38       <citerefentry><refentrytitle>systemd.device</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
  39       <citerefentry><refentrytitle>systemd.mount</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
  40       <citerefentry><refentrytitle>systemd.automount</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
  41       <citerefentry><refentrytitle>systemd.swap</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
  42       <citerefentry><refentrytitle>systemd.target</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
  43       <citerefentry><refentrytitle>systemd.path</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
  44       <citerefentry><refentrytitle>systemd.timer</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
  45       <citerefentry><refentrytitle>systemd.slice</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
  46       <citerefentry><refentrytitle>systemd.scope</refentrytitle><manvolnum>5</manvolnum></citerefentry></para></listitem>
  47
  48       <listitem><para>daemon config files, see
  49       <citerefentry><refentrytitle>systemd-system.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
  50       <citerefentry><refentrytitle>systemd-user.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
  51       <citerefentry><refentrytitle>logind.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
  52       <citerefentry><refentrytitle>journald.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
  53       <citerefentry><refentrytitle>journal-remote.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
  54       <citerefentry><refentrytitle>journal-upload.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
  55       <citerefentry><refentrytitle>systemd-sleep.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
  56       <citerefentry><refentrytitle>timesyncd.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>
  57       </para></listitem>
  58     </itemizedlist>
  59     </para>
  60
  61     <para>The syntax is inspired by
  62     <ulink url="http://standards.freedesktop.org/desktop-entry-spec/latest/">XDG Desktop Entry Specification</ulink>
  63     <filename>.desktop</filename> files, which are in turn inspired by Microsoft Windows
  64     <filename>.ini</filename> files.
  65     </para>
  66
  67     <para>Each file is a plain text file divided into sections, with configuration entries in the
  68     style <replaceable>key</replaceable>=<replaceable>value</replaceable>.
  69     Empty lines and lines starting with <literal>#</literal> or <literal>;</literal> are
  70     ignored, which may be used for commenting.</para>
  71
  72     <para>Lines ending in a backslash are concatenated with the following line while reading and the
  73     backslash is replaced by a space character. This may be used to wrap long lines. The limit on
  74     line length is very large (currently 1 MB), but it is recommended to avoid such long lines and
  75     use multiple directives, variable substitution, or other mechanism as appropriate for the given
  76     file type. When a comment line or lines follow a line ending with a backslash, the comment block
  77     is ignored, so the continued line is concatenated with whatever follows the comment block.</para>
  78
  79     <example><programlisting>[Section A]
  80 KeyOne=value 1
  81 KeyTwo=value 2
  82
  83 # a comment
  84
  85 [Section B]
  86 Setting="something" "some thing" "…"
  87 KeyTwo=value 2 \
  88        value 2 continued
  89
  90 [Section C]
  91 KeyThree=value 2\
  92 # this line is ignored
  93 ; this line is ignored too
  94        value 2 continued
  95 </programlisting></example>
  96
  97     <para>Boolean arguments used in configuration files can be written in
  98     various formats. For positive settings the strings
  99     <option>1</option>, <option>yes</option>, <option>true</option>
 100     and <option>on</option> are equivalent. For negative settings, the
 101     strings <option>0</option>, <option>no</option>,
 102     <option>false</option> and <option>off</option> are
 103     equivalent.</para>
 104
 105     <para>Time span values encoded in configuration files can be written in various formats. A stand-alone
 106     number specifies a time in seconds.  If suffixed with a time unit, the unit is honored. A
 107     concatenation of multiple values with units is supported, in which case the values are added
 108     up. Example: <literal>50</literal> refers to 50 seconds; <literal>2min 200ms</literal> refers to
 109     2 minutes and 200 milliseconds, i.e. 120200 ms.  The following time units are understood:
 110     <literal>s</literal>, <literal>min</literal>, <literal>h</literal>, <literal>d</literal>,
 111     <literal>w</literal>, <literal>ms</literal>, <literal>us</literal>.  For details see
 112     <citerefentry><refentrytitle>systemd.time</refentrytitle><manvolnum>7</manvolnum></citerefentry>.</para>
 113
 114     <para>Various settings are allowed to be specified more than once, in which case the
 115     interpretation depends on the setting. Often, multiple settings form a list, and setting to an
 116     empty value "resets", which means that previous assignments are ignored. When this is allowed,
 117     it is mentioned in the description of the setting. Note that using multiple assignments to the
 118     same value makes the file incompatible with parsers for the XDG <filename>.desktop</filename>
 119     file format.</para>
 120   </refsect1>
 121
 122   <refsect1>
 123     <title>See Also</title>
 124     <para>
 125       <citerefentry><refentrytitle>systemd.time</refentrytitle><manvolnum>7</manvolnum></citerefentry>
 126     </para>
 127   </refsect1>
 128
 129 </refentry>